530 research outputs found
Incorporating metals into de novo proteins
The de novo design of artificial metalloproteins from first-principles is a powerful strategy with which to establish the minimum structure required for function, as well as to identify the important design features for tuning the chemistry of the coordinated metal ion. Herein we describe recent contributions to this field, covering metallo-porphyrin, mononuclear and multinuclear metal ion sites engineered into de novo proteins. Using miniature artificial scaffolds these examples demonstrate that complex natural protein folds are not required to mimic naturally occurring metal ion sites in proteins. More importantly progress is being made to engineer de novo metalloproteins capable of performing functions not in the repertoire of biology
Semiconductor optical fibres for infrared applications: a review
Over the last decade a new class of optical fibre has emerged that incorporates semiconductor materials within the core. These fibres are rich in optoelectronic functionality and offer extended transmission bands across the infrared spectral region so that their application potential is vast. Various fabrication methods have been developed to produce fibres with a range of unary and compound semiconductor core materials, which can be either amorphous or crystalline in form. This review discusses the main fabrication procedures and the infrared optical properties of the semiconductor fibres that have been fabricated to date, then takes a look at the future prospects of this exciting new technology
Flat-top temperature tuning response in periodically-poled nonlinear crystals
Second harmonic generation via periodically-poled nonlinear materials offers an efficient means of generating high-quality visible light that would be otherwise unattainable with traditional laser sources. While this technology has the potential for implementation in many mass-industrial applications, temperature stability requirements of 0.1 deg.C can make packaging with a pump source problematic. Using our high fidelity poling technique we have achieved precise placement of poled domains in Lithium Niobate based on the resulting mathematical models. These initial devices provide more than 4 deg.C flat-top temperature stability, albeit with a corresponding loss in operational efficiency. Our aim is to implement improved designs in magnesium-doped Lithium Niobate for packaging with near-room temperature diode-based pump sources, as could be applied towards RGB TV and projector applications
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Non-isothermal phase-field simulations of laser-written in-plane SiGe heterostructures for photonic applications
Advanced solid-state devices, including lasers and modulators, require semiconductor heterostructures for nanoscale engineering of the electronic bandgap and refractive index. However, existing epitaxial growth methods are limited to fabrication of vertical heterostructures grown layer by layer. Here, we report the use of finite-element-method-based phase-field modelling with thermocapillary convection to investigate laser inscription of in-plane heterostructures within silicon-germanium films. The modelling is supported by experimental work using epitaxially-grown Si0.5Ge0.5 layers. The phase-field simulations reveal that various in-plane heterostructures with single or periodic interfaces can be fabricated by controlling phase segregation through modulation of the scan speed, power, and beam position. Optical simulations are used to demonstrate the potential for two devices: graded-index waveguides with Ge-rich (>70%) cores, and waveguide Bragg gratings with nanoscale periods (100–500 nm). Periodic heterostructure formation via sub-millisecond modulation of the laser parameters opens a route for post-growth fabrication of in-plane quantum wells and superlattices in semiconductor alloy films
Probing the missing baryons with the Sunyaev-Zel'dovich effect from filaments
Observations of galaxies and galaxy clusters in the local universe can
account for only of the total baryon content. Cosmological
simulations predict that the `missing baryons' are spread throughout
filamentary structures in the cosmic web, forming a low-density gas with
temperatures of K. We search for this warm-hot intergalactic
medium (WHIM) by stacking the Planck Compton -parameter map of the thermal
Sunyaev-Zel'dovich (tSZ) effect for 1,002,334 pairs of CMASS galaxies from the
Sloan Digital Sky Survey. We model the contribution from the galaxy halo pairs
assuming spherical symmetry, finding a residual tSZ signal at the
2.9\mbox{\sigma} level from a stacked filament of length with a Compton parameter magnitude . We
consider possible sources of contamination and conclude that bound gas in
haloes may contribute only up to of the measured filamentary signal. To
estimate the filament gas properties we measure the gravitational lensing
signal for the same sample of galaxy pairs; in combination with the tSZ signal,
this yields an inferred gas density of with a temperature K. This result is consistent with the predicted WHIM properties, and
overall the filamentary gas can account for of the total baryon
content of the Universe. We also see evidence that the gas filament extends
beyond the galaxy pair. Averaging over this longer baseline boosts the
significance of the tSZ signal and increases the associated baryon content to
of the global value.Comment: 13 pages, 8 figures; accepted for publication in A&
Towards in-fiber silicon photonics
We review the recent advancements in the fabrication and application of silicon optical fibers. Particular focus is placed on novel materials and device designs for use in optical signal processing systems
Semiconductor optical fibers
We review the recent advancements in the fabrication and application of semiconductor optical fibers. Particular focus is placed on novel materials and device designs for use in optical signal processing systems
Graphene-based fiber polarizer with PVB-enhanced light interaction
Graphene is a two-dimensional material which, as a result of its excellent photonic properties, has been investigated for a wide range of optical applications. In this paper, we propose and fabricate a commercial grade broadband graphene-based fiber polarizer using a low loss side-polished optical fiber platform. A high index polyvinyl butyral layer is used to enhance the light-graphene interaction of the evanescent field of the core guided mode to simultaneously obtain a high extinction ratio ~37.5 dB with a low device loss ~1 dB. Characterization of the optical properties reveals that the polarizer retains low transmission losses and high extinction ratios across an extended telecoms band. The results demonstrate that side-polished fibers are a useful platform for leveraging the unique properties of low-dimensional materials in a robust and compact device geometry
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